Method of an means for recognizing signal edges

ABSTRACT

In the case of a method of detecting a signal edge in a signal with temporally successive signal edges, there are performed, after triggering by an interrupt signal (IS) generated in an analog/digital converter ( 13 ), detection of a rise-representing rise value between two detected amplitude values with subsequent assessment of the rise value together with detection of signal edge direction information and signal edge occurrence information. Further use of this signal edge information is dependent on an additionally detected and assessed signal strength value, which signal strength value is formed from a sum of further amplitude values.

The invention relates to a method of detecting a signal edge in a signalwith temporally successive signal edges, in which method the methodsteps listed below are performed, namely:

-   a) etection of temporally successive amplitude values of the signal,-   b) etection of the presence of a rise between a first detected    amplitude value and a second detected amplitude value,-   c) etection of signal edge occurrence information representing the    time of occurrence of a signal edge.

The invention further relates to a communication station and to signaledge detection means, which are suitable for performing such a method.

Such signal edge detection means, which are suitable for performing amethod with the above-mentioned method steps of detecting signal edgesin a signal with temporally successive signal edges, are known frompatent document U.S. Pat. No. 5,293,369 A, for example. With the knownsolution, it is already known to sample an analog signal by means of anA/D converter and to generate digital data, which digital data representa signal amplitude value. It is also already known to ascertainovershooting or undershooting of amplitude values of the signal of thedigitized signal in relation to a signal amplitude threshold and toascertain a signal amplitude threshold overshoot time between twosuccessive amplitude values of the signal, if a first signal amplitudevalue lies below the signal amplitude threshold and a following secondsignal amplitude value lies over the signal amplitude threshold. It isalso already known from the known solution to assess a rise of anoccurring signal edge in relation to a rise threshold. However, theknown solution is unfortunately not sufficient to detect signal edges ina signal with temporally successive signal edges when interferencepulses additionally occur in the signal and the signal is relativelyweak and relatively noisy. Such a signal occurs for example in an RFIDsystem. Something that is particularly difficult in such an RFID systemis the detection of the signal edges in a signal with temporallysuccessive signal edges, if a data signal transmission means suitablefor performing load modulation, for example a data carrier forcontactless communication, is produced by means of a semi-conductingpolymer. The reason for this is that, in this case, only limited loadmodulation may be performed due to the marked scattering of individualcomponents of the data signal transmission means made from asemi-conducting polymer and due to a pronounced ageing effect of thecomponents, which limited load modulation leads ultimately to arelatively small signal, wherein the detection of signal edges can thenno longer proceed satisfactorily with the known solution.

It is an object of the invention to eliminate the above-describedproblems and to provide an improved method and an improved communicationstation and improved signal edge detection means.

To achieve the above-mentioned object, features according to theinvention are provided for a method according to the invention, suchthat a method according to the invention may be characterized in thefollowing way, namely:

A method of detecting a signal edge in a signal with temporallysuccessive signal edges, in which method the method steps listed beloware performed, namely:

-   a) etection of temporally successive amplitude values of the signal,-   b) etection of the presence of a rise between a first detected    amplitude value and a second detected amplitude value,-   c) etection of signal edge occurrence information representing the    time of occurrence of a signal edge,-   d) etection of a signal strength value by means of at least one of    the detected amplitude values,-   e) assessment of the detected signal strength value in relation to a    signal strength reference value.

To achieve the above-mentioned object, features according to theinvention are provided for a communication station according to theinvention, so that a communication station according to the inventionmay be characterized in the following way, namely:

A communication station with signal edge detection means for detecting asignal edge in a signal with temporally successive signal edges, whichsignal edge detection means comprise means listed below, namely:

-   a) amplitude value detection means for the detection of temporally    successive amplitude values of the signal,-   b) rise detection means for the detection of the presence of a rise    between a first detected amplitude value and a second detected    amplitude value,-   c) time of occurrence detection means for the detection of signal    edge occurrence information representing the time of occurrence of a    signal edge,-   d) signal strength value detection means for the detection of a    signal strength value by means of at least one of the detected    amplitude values,-   e), signal strength value assessment means for the assessment of the    detected signal strength value in relation to a signal strength    reference value.

To achieve the above-mentioned object, features according to theinvention are provided for signal edge detection means according to theinvention, so that signal edge detection means according to theinvention may be characterized in the following way, namely:

Signal edge detection means for detecting a signal edge in a signal withtemporally successive signal edges, which signal edge detection meanscomprise means listed below, namely:

-   a) amplitude value detection means for the detection of temporally    successive amplitude values of the signal,-   b) rise detection means for the detection of a rise between a first    detected amplitude value and a second detected amplitude value,-   c) time of occurrence detection means for the detection of signal    edge occurrence information representing the time of occurrence of a    signal edge,-   d) signal strength value detection means for the detection of a    signal strength value by means of at least one of the detected    amplitude values,-   e) signal strength value assessment means for the assessment of the    detected signal strength value in relation to a signal strength    reference value.

By providing the features according to the invention, an improved methodand an improved communication station and improved signal edge detectionmeans are obtained in a simple way and using both a hard-wired logiccircuit and a programmable circuit, wherein a very important improvementconsists in the fact that, with the method according to the invention,an improvement in interference susceptibility is achieved with regard tothe detection of signal edges in a data signal. An advantage is achievedfor example in particular in the case of RFID data transmission systems,in which a modulated data signal is output by a data signal transmissionmeans made by the so-called polymer-IC technique, wherein the modulateddata signal is then output in relatively weak form, whereby only arelatively noisy demodulated data signal arises in a communicationstation receiving the modulated data signal after demodulation of thisdata signal but problem-free data communication with the communicationstation is nonetheless always ensured by the provision of the measuresaccording to the invention, since, by means of the measures according tothe invention, problem-free detection of signal edges of the demodulateddata signal is ensured despite the relatively weak modulated data signaland the relatively noisy demodulated data signal. A particular advantageof the method according to the invention is obtained when interferencepulses or spikes occur, i.e. a superimposed interference signal occurs,in a signal with temporally successive signal edges, i.e. a conventionalwanted signal, since in this case in particular detection of the wantedsignal edges proceeds correctly.

In the case of a method according to the invention, it has provenparticularly advantageous for the features as claimed in claim 2 orclaim 3 or claim 4 to be additionally provided, since in all of thesecases a signal strength value is obtained relatively simply andsufficiently precisely.

It has moreover proven advantageous, in connection with theabove-described measures according to the invention, for the features asclaimed in claim 5 or claim 6 to be additionally provided. Thesemeasures known per se are particularly advantageous in the context ofthe present invention.

The above-stated aspects of the invention and further aspects thereofemerge from the example of embodiment described below and are explainedwith reference to this example of embodiment.

The invention will be further described with reference to an example ofembodiment shown in the drawings, to which, however, the invention isnot restricted.

FIG. 1 is a schematic representation, in the form of a block diagram, ofa portion, essential in the present context, of a communication stationand of signal edge detection means according to an example of embodimentof the invention.

FIG. 2 shows a flow chart of a routine, which is performed in thecommunication station as shown in FIG. 1 when a method according to theinvention is implemented.

FIG. 3 is a schematic representation of a portion of a data signaloccurring in the communication station according to FIG. 1 and theinformation obtained therefrom.

FIG. 1 shows a communication station 1. The communication station 1comprises a station circuit 2, which in the present instance takes theform of a microcomputer. It should be mentioned that the station circuit2 may also take the form of a hard-wired logic circuit. The stationcircuit 2 comprises a central processing unit (CPU) 4 and furthercomponents which are not shown but which are required for standardoperation of a microcomputer, together with station data processingmeans 5, which station data processing means 5 are controlled by thecentral processing unit (CPU) 4.

The station circuit 2 further comprises data rate detection means 3,which data rate detection means 3 are likewise controlled by the centralprocessing unit (CPU) 4 and are provided for performing data ratedetection. The data rate detection means 3 comprise signal edgedetection means 6, which are designed to detect signal edges, and inthis case rising signal edges, and to generate signal edge occurrenceinformation SFAI. It should be mentioned that such signal edge detectionmeans 6 are also designed to detect falling signal edges, as will becomeobvious from the remainder of the description. In addition, monitoringmeans 7 are contained in the data rate detection means 3, to whichmonitoring means 7 the signal edge occurrence information SFAI is fedand which monitoring means 7 are designed to monitor signal edge timesof occurrence within given limits. Signal edge expected-time windowinformation EFAI may be fed by the monitoring means 7 to the signal edgedetection means 6. The data rate detection means 3 are further designedto output detected data ED to the station data processing means 5.

The signal edge detection means 6 contain memory means 15, to whichmemory means 15 amplitude value information AI is fed and which memorymeans 15 are designed to store amplitude value information. The memorymeans 15 may also be memory means 15 which are external relative to thesignal edge detection means 6. Downstream of the memory means 15 areconnected rise detection means 8, which are designed to detect thepresence of a rise of a signal edge, and threshold detection means 9,which are provided for calculating amplitude thresholds +THL and −THL,and time of occurrence detection means 10, which are designed to detectsignal edge occurrence information SFAI, and signal strength valuedetection means 12, which are designed to detect a signal strengthvalue. Signal strength value assessment means 13 are contained in thesignal strength value detection means 12, which signal strength valueassessment means 13 are designed to assess a signal strength value.Downstream of the rise detection means 8 are connected directiondetection means 11, which direction detection means 11 are designed todetect signal edge direction information.

The communication station 1 is in the present case a component of anasynchronous data transmission system and is in this respect designedfor contactless communication with at least one data carrier, notdescribed here. This contactless communication may proceed for exampleat least in part to ISO standard 14443. To this end, the communicationstation 1 further comprises transmit/receive means 16 for transmittingand receiving data signals respectively to and from at least one datacarrier and demodulation means 17, which demodulation means 17 areconnected with the transmit/receive means 16 and designed to demodulatethe signal supplied by the transmit/receive means 16. The means requiredfor transmitting operation are not shown, due to their irrelevance inthe present context. In the case of the present communication station 1,the transmit/receive means 16 are designed respectively to transmit orreceive data signals in capacitive manner. It should be mentioned thatthe transmit/receive means 16 may also be designed in inductive mannerfor transmission or reception. A demodulated data signal obtained bymeans of the demodulation means 17 and which occurs in theabove-mentioned asynchronous data transmission system, in whichasynchronous data transmission system a bit is transmitted in the formof a signal edge generated at a specific set time, is fed to amplitudevalue detection means 14, which are downstream of the demodulation means17. The amplitude value detection means 14 are designed to detectamplitude values and to output amplitude value information AI and tooutput an interrupt signal IS. In the case of the communication station1 of FIG. 1, the amplitude value detection means 14 take the form of ananalog/digital converter formed with the microcomputer, whichanalog/digital converter outputs amplitude value information AI in theform of 10 bit-wide data with a specific sampling frequency to thememory means 15. The interrupt signal IS is formed after eachanalog/digital conversion performed by the analog/digital converter andfed to the central processing unit (CPUT) 4. The sampling frequency orsampling rate is in the present case ten thousand (10,000) samplings persecond, which corresponds to a sampling frequency of approximately 10samplings per transmitted bit, i.e. each in the form of a signal edgegenerated at a specific set time. It may be mentioned that, ifdesirable, the sampling frequency may be substantially higher, forexample twice or three times the stated sampling frequency, or lower,for instance half the stated sampling frequency.

A sequence will now be described below, which is performed in themicrocomputer and in particular in the signal edge detection means 16after activation by the central processing unit (CPU) 4 on the basis ofan interrupt signal IS. By way of explanation, reference should here bemade to FIG. 2, which FIG. 2 shows detected amplitude values M1, M2, M3,M4, M5, which are in each case separated from one another by a samplingtime interval ts, together with the amplitude threshold +THL and aninterpolation curve EL and a signal edge time of occurrence SFA and acorrection value K.

Reference should in principle be made to the fact that the describedsequence may proceed repeatedly and in succession and that, during thesequence, variables assume assigned values, which assigned values maymaintain their validity in a following sequence.

As is clear from FIG. 2, the sequence is begun at a block 20.Calculation of the amplitude threshold +THL then proceeds at a block 21by means of the threshold detection means 9. In the present case, anenvelope curve of the demodulated data signal is used for calculation ofthe amplitude threshold +THL. More precisely, the amplitude threshold+THL is formed from half the difference between a maximum envelope curvevalue and a minimum envelope curve value. It may be mentioned that theamplitude threshold +THL may also be formed by other values, but this isknown in expert circles and will not for this reason be examined in anymore detail here. After the block 21, an interrogation is performed at ablock 22 as to whether a positive or a negative signal edge is to bedetected, by interrogating a NEXTEDGE variable for a POS value. If theresult of the interrogation at block 22 is positive (YES), the sequenceis continued at a block 23, i.e. is branched for signal edge detectionof a positive signal edge by means of the signal edge detection means 6.If the result is negative (NO), the sequence continues at block 28, i.e.is branched for signal edge detection of a negative signal edge.

At block 23, an interrogation is performed by means of the risedetection means 8 as to whether the amplitude value M2 detected by meansof the amplitude value detection means 14 and stored in the memory means15 is greater than or equal to the amplitude threshold +THL. If theresult of the interrogation at block 23 is positive (YES), the sequenceis continued at a block 24, whereas, if the result is negative (NO), thesequence is broken off, i.e. a new interrupt signal is awaited. At theblock 24, an interrogation is performed by means of the rise detectionmeans 8 as to whether the detected amplitude value M1 is lower than theamplitude threshold +THL. If the result of the interrogation at block 24is positive (YES), the sequence is continued at a block 25, whereas, ifthe result is negative (NO), the sequence is again broken off. At theblock 25, a calculation of a signal strength value S from the detectedamplitude values M2, M3, M4 and M5 is effected by means of the signalstrength value detection means 12 and on the basis of the equationS=M2+M3+M4+M5  (1)

It may be mentioned that for calculation of the signal strength value S,it is also possible to use fewer detected amplitude values, for exampleonly the detected amplitude values M2 and M3, or indeed if necessarymore detected amplitude values, for example in addition to the detectedamplitude values M2, M3, M4 and M5, further detected amplitude valueswhich are not shown but which would be designed in FIG. 3 with referencenumerals M6 and M7. It should additionally be mentioned that the signalstrength value S may be formed from the differences between the detectedamplitude values used for calculation and the amplitude threshold +THL,for example in accordance with the following equation:S=[M2−(+THL)]+[M3−(+THL)]  (2)

In the present case, after block 25 a check is performed at a block 26,by means of the signal strength value assessment means 13, as to whetherthe signal strength value S is greater than a signal strength referencevalue, wherein in the present case the signal strength reference valueamounts to four times the amplitude threshold +THL. Express referenceshould be made to the fact that the signal strength reference value mayalso assume other values, for example five times or twice the amplitudethreshold +THL, wherein this may depend also on how strong interferenceamplitudes are in comparison to the signal amplitudes, and how steep anexpected signal edge is in comparison with interference variations inrelation to the sampling rate. If the result of the interrogation atblock 26 is positive (YES), the sequence is continued at a block 27,whereas, if the result is negative (NO), the sequence is again brokenoff. At the block 27, signal edge direction information is formed bymeans of the direction detection means 11. In the present case, thesignal edge direction information is formed in that the NEXTEDGEvariable is set to a NEG value, thereby causing a negative signal edgeto be detected during a rerun of the sequence, wherein the sequence isthen continued at a block 28. At the block 27, calculation of the signaledge time of occurrence SFA additionally is additionally effected bymeans of the time of occurrence detection means 10, as shown in FIG. 3.To this end, a correction value K is calculated as follows from a linearinterpolation between the detected amplitude value M1 and the detectedamplitude value M2 separated by the sampling time interval ts:

$\begin{matrix}{K = \frac{\left( {{M2} - \left( {+ {THL}} \right)} \right)*{ts}}{\left( {{M2} - {M1}} \right)}} & (3)\end{matrix}$

It may be mentioned that the correction value K may also be detected ina different manner, for example by performing other interpolationmethods, as known in specialist circles and therefore not examined inany more detail here. After the block 27, the sequence is continued at ablock 33, which will be examined in more detail below.

In the case of signal edge detection of a negative signal edge by meansof the signal edge detection means 6, as described below, referenceshould once again be made to FIG. 3, wherein the assumption should bemade that the ordinate illustrated represents a negative direction and aportion of a negative signal edge is thus illustrated. At theabove-mentioned block 28, an interrogation is now performed as towhether the amplitude value M2 detected by means of the amplitude valuedetection means 14 and stored in the memory means 15 is lower than orequal to a negative amplitude threshold −THL, wherein the negativeamplitude threshold −THL is in this case equal in value to the positiveamplitude threshold +THL. If the result of the interrogation at block 28is positive (YES), the sequence is continued at a block 29, whereas, ifthe result is negative (NO), the sequence is broken off, i.e. a newinterrupt signal is awaited. At the block 29, an interrogation isperformed as to whether the detected amplitude value M1 is greater thanthe negative amplitude threshold −THL. If the result of theinterrogation at block 29 is positive (YES), the sequence is continuedat a block 30, whereas, if the result is negative (NO), the sequence isagain broken off. At the block 30, a calculation of a signal strengthvalue S from the detected amplitude values M2, M3, M4 and M5 iseffected, as in the case of signal edge detection of a positive signaledge, on the basis of the equation:S=M2+M3+M4+M5  (4)

Thereafter, a check is performed at a block 31, by means of the signalstrength value detection means 12, as to whether the signal strengthvalue S is greater than a signal strength reference value, wherein inthe present case the signal strength reference value amounts to fourtimes the amplitude threshold −THL. Reference should at this point againbe made to the fact that the signal strength reference value may alsoassume other values, as was mentioned with reference to signal edgedetection of a positive signal edge. If the result of the interrogationat block 31 is positive (YES), the sequence is continued at a block 32,whereas, if the result is negative (NO), the sequence is again brokenoff. At the block 32, signal edge direction information is againobtained by means of the direction detection means 11 in such a way thatthe NEXTEDGE variable is set to a POS value, thereby causing a positivesignal edge to be detected during a rerun of the sequence. At the block32, calculation of the signal edge time of occurrence SFA isadditionally effected by means of the time of occurrence detection means10. To this end, a correction value K is calculated as follows from alinear interpolation between the detected amplitude value M1 and thedetected amplitude value M2 separated by the sampling time interval ts:

$\begin{matrix}{K = \frac{\left( {{M2} + \left( {- {THL}} \right)} \right)*{ts}}{\left( {{M2} - {M1}} \right)}} & (5)\end{matrix}$

After the block 27, the sequence is continued at a block 33. In theblock 33, data rate detection proceeds as described in the as yetunpublished European patent application bearing application no. 01 890214.8 and bearing the applicant's reference PHAT010044 EP-P, wherein thepreviously detected signal edge time of occurrence SFA required for thesequence described here is forwarded. After the block 33, the sequenceis finally completed at a block 34.

It may be mentioned that the rise detection means 8 may also containrise assessment means, with which rise assessment means a rise may beassessed with regard to the rise value thereof. The provision of suchrise assessment means offers the advantage that signal edges with tooslight a degree of rise may be simply eliminated thereby, such that suchsignal edges do not undergo any detection process.

It should additionally be mentioned that, in the case of a modificationof the above-described sequence, the signal edge expected-time windowinformation EFAI, which defines a time window and which may be generatedby means of the monitoring means and output by the monitoring means 7,is used in the communication station 1 according to FIG. 1 to allowdetection of signal edges only in the time window defined by thisinformation EFAI. By this measure, the detection reliability in the caseof a method according to the invention is additionally improved.

1. A method of detecting a signal edge in a signal with temporallysuccessive signal edges, the method comprising: a) detection oftemporally successive amplitude values of the signal, b) detection ofthe presence of a rise between a first detected amplitude value and asecond detected amplitude value, c) detection of signal edge occurrenceinformation representing the time of occurrence of a signal edge, d)detection of a signal strength value by means of at least one of thedetected amplitude values, e) assessment of the detected signal strengthvalue in relation to a signal strength reference value.
 2. A method asclaimed in claim 1, in which the signal strength value is obtained fromthe absolute value of the difference between the at least one detectedamplitude value and an amplitude threshold for the signal.
 3. A methodas claimed in claim 1, in which the signal strength value is detected bymeans of least one amplitude value lying outside a time period betweenthe first detected amplitude value and he second detected amplitudevalue.
 4. A method as claimed in claim 1, in which the signal strengthvalue is detected by sum formation from at least one of the firstdetected amplitude value and the second detected amplitude value and atleast one further amplitude value.
 5. A method as claimed in claim 4, inwhich an assessment of the detected rise with regard to its rise valuein relation to a rise threshold is performed and in which detection ofsignal edge direction information representing the direction of a signaledge is performed, in which positive signal edge direction informationis formed if the first amplitude value is lower than the amplitudethreshold and the second amplitude value occurs after the first detectedamplitude value and is greater than the amplitude threshold and if thesum of the difference between the second detected amplitude value andthe amplitude threshold and at least a further difference between afurther amplitude value subsequent to the second detected amplitudevalue and the amplitude threshold is greater than the signal strengthreference value.
 6. A method as claimed in claim 4, in which aninterpolation curve is set between the first detected amplitude valueand the second detected amplitude value and in which the signal edgeoccurrence information is determined by means of the amplitude value,coinciding with the amplitude threshold, of the interpolation curve. 7.A communication station with signal edge detection means for detecting asignal edge in a signal with temporally successive signal edges, whichsignal edge detection means comprises: a) amplitude value detectionmeans for the detection of temporally successive amplitude values of thesignal, b) rise detection means for the detection of the presence of arise between a first detected amplitude value and a second detectedamplitude value, c) time of occurrence detection means for the detectionof signal edge occurrence information representing the time ofoccurrence of a signal edge, d) signal strength value detection meansfor the detection of a signal strength value by means of at least one ofthe detected amplitude values, e) signal strength value assessment meansfor the assessment of the detected signal strength value in relation toa signal strength reference value.
 8. Signal edge detection means fordetecting a signal edge in a signal with temporally successive signaledges, which signal edge detection means comprises: a) amplitude valuedetection means for the detection of temporally successive amplitudevalues of the signal, b) rise detection means for the detection of arise between a first detected amplitude value and a second detectedamplitude value, c) time of occurrence detection means for the detectionof signal edge occurrence information representing the time ofoccurrence of a signal edge, d) signal strength value detection meansfor the detection of a signal strength value by means of at least one ofthe detected amplitude values, e) signal strength value assessment meansfor the assessment of the detected signal strength value in relation toa signal strength reference value.